ENTRAINMENT AND MODIFICATION OF MANTLE CARGO Decompression during kimberlite ascent induces inter... more ENTRAINMENT AND MODIFICATION OF MANTLE CARGO Decompression during kimberlite ascent induces internal stresses in xenoliths requiring volume expansion. High ascent rates imply rapid decompression rates that will exceed normal rates of ductile relaxation in xenoliths. The internal elastic stresses will accumulate promoting tensile failure to produce smaller xenoliths and xenocrysts. Residual stresses (∆σR) depend on ascent velocity (U), the bulk modulus (KT) and viscosity (μ) of the xenolith, and the pressure drop over the ascent distance [z – z0]:
The Atlin Integrated Geoscience Project, jointly funded by federal and provincial governments, en... more The Atlin Integrated Geoscience Project, jointly funded by federal and provincial governments, entered its third and final year in 2002–2003. It is designed to advance understanding of the geological evolution and mineral potential of the northern Cache Creek terrane. Project accomplishments for year three include 1) characterization of Cache Creek Group biostratigraphy and tectonostratigraphy; 2) new surficial geology map outlining placer potential in the Atlin area; 3) improved understanding of the age, composition, emplacement, and metallogenic potential of Mesozoic plutonic rocks; 4) better definition of the distribution and paleoenvironment of Neogene volcanism; 5) delivery of a one-day workshop on magnetic surveying to prospectors and the general public. High-grade copper mineralization was discovered by personnel from the provincial survey. The discovery, named Joss’alun, is hosted within oceanic crustal rocks of the Cache Creek terrane. Mineralization appears concordant with the enclosing volcanic stratigraphy. If syngenetic, it establishes the terrane’s volcanogenic massive sulphide potential. Page 1 Resume : Le projet d’Atlin de l’Initiative geoscientifique ciblee, dont le financement est assure conjointement par les gouvernements federal et provincial, en est a sa troisieme et derniere annee en 2002-2003. Il vise a ameliorer notre comprehension de l’evolution geologique et du potentiel mineral de la partie nord du terrane de Cache Creek. Pendant les trois annees du projet il a ete possible 1) de caracteriser le Groupe de Cache Creek des points de vue biostratigraphique et tectonostratigraphique; 2) de dresser une nouvelle carte geologique des materiaux superficiels delimitant les aires potentielles de placer dans la region d’Atlin; 3) d’ameliorer notre comprehension de l’âge, de la composition, de la mise en place et du potentiel metallogenique des roches plutoniques du Mesozoique; 4) de mieux definir la distribution et le paleoenvironnement du volcanisme neogene; 5) de tenir un atelier d’une duree d’une journee sur les leves magnetiques a l’intention des prospecteurs et du grand public. Une mineralisation cuprifere a haute teneur a ete identifiee par le personnel des services geologiques provinciaux. Cette mineralisation, a laquelle a ete attribue le nom de Joss’alun, est encaissee dans les roches de croute oceanique du terrane de Cache Creek. Par rapport a la stratigraphie volcanique encaissante, la mineralisation semble presenter une relation de concordance. Si elle se revele syngenetique, ceci etablirait pour le terrane un certain potentiel quant aux mineralisations de sulfure massifs volcanogenes. 1 Contribution to the Targeted Geoscience Initiative (TGI) 2000–2003.
... Specifically, we have used the point load strength test (PLST) to measure rock strength and, ... more ... Specifically, we have used the point load strength test (PLST) to measure rock strength and, thereby, track welding intensity in a section of the Bandelier Tuff (Smith & Bailey, 1966; Broxton & Reneau, 1995). PLST is an ideal technique for field studies (eg, Broch & Franklin, 1972 ...
... o.oo INSIGHTS ON WWWBASED GEOSCIENCE TEACHING: CLIMBING THE FIRST YEAR LEARNING CLIFF MICHELL... more ... o.oo INSIGHTS ON WWWBASED GEOSCIENCE TEACHING: CLIMBING THE FIRST YEAR LEARNING CLIFF MICHELLE N. LAMBERSON, MARK JOHNSON, MARY ... with instructors and other students, a site to do selfpaced, directed exercises on important petrolo gic concepts ...
Fine-grained gouge (< 5 microns) is generated along shear zones during the emplacement of daci... more Fine-grained gouge (< 5 microns) is generated along shear zones during the emplacement of dacite domes during the most recent volcanic activity at Mount Saint Helens. Here, we present grain size data from both the natural fault rocks from Mount Saint Helen's and experimentally generated gouge. Our triaxial rock deformation experiments were run at confining pressures (Pc) of 0, 25, 50, and 75MPa, at room temperature and strain rates of ~1 x 10-4/s. We performed experiments that were terminated after failure and experiments on frictional sliding of the gouge. Our starting material has low (6-8%) porosities, a uniform bulk composition (65 wt% SiO2) and is highly. The dacite experiments show a progressive increase in peak strength (100-700 MPa) with increasing Pc and all cores show brittle behavior, characterized by a rapid stress drop. Run products contain macroscopic fractures with deformation extremely localized around the shear fractures. Experimentally deformed dacites show extreme grain size reduction and the production of gouge. Gouge material can reach < 1 micron in diameter. Frictional sliding experiments generated more gouge than experiments stopped after failure. However, there is little modification of the finest grain sizes (<20 microns) because of frictional sliding. We propose that the large stress drop at failure generates the fine-grained gouge and subsequent sliding does not further reduce the grain size. The amount of energy required to produce the fine-grained material is calculated and we compare this to the energy required to generate volcanic ash from fragmentation.
Kimberlite rocks and deposits are the eruption products of volatile-rich, silica-poor ultrabasic ... more Kimberlite rocks and deposits are the eruption products of volatile-rich, silica-poor ultrabasic magmas that originate as small-degree mantle melts at depths in excess of 200 km. Many kimberlites are emplaced as subsurface cylindrical-to-conical pipes and associated sills and dykes. Surficial volcanic deposits of kimberlite are rare. Although kimberlite magmas have distinctive chemical and physical properties, their eruption styles, intensities and durations are similar to conventional volcanoes. Rates of magma ascent and transport through the cratonic lithosphere are informed by mantle cargo entrained by kimberlite, by the geometries of kimberlite dykes exposed in diamond mines, and by laboratory-based studies of dyke mechanics. Outstanding questions concern the mechanisms that trigger and control the rates of kimberlite magmatism.
A recent volcanic eruption occurred at Tseax volcano that formed a series of tephra cones in nort... more A recent volcanic eruption occurred at Tseax volcano that formed a series of tephra cones in northwestern British Columbia, Canada. The explosive to effusive eruption also formed a 32 km long sequence of Fe-rich Mg-poor basanite–trachybasalt lavas covering ∼40 km2. Oral histories of the Nisg_a’a Nation report that the eruption may have caused as many as 2000 fatalities. The actual eruption date and question of whether there was one or multiple eruptive episodes in the 14th and 18th centuries are, as of yet, unresolved. New radiocarbon dating of wood charcoal from immediately beneath vent-proximal tephra deposits and complementary age information suggest an eruption in 1675–1778 CE (95.4% probability) was responsible for the formation of the tephra cone. New paleomagnetic and geochemical data from the tephra cone and lava flows suggest there is, in fact, no statistically significant difference in time between the explosive and effusive deposits and that they formed during a single er...
ENTRAINMENT AND MODIFICATION OF MANTLE CARGO Decompression during kimberlite ascent induces inter... more ENTRAINMENT AND MODIFICATION OF MANTLE CARGO Decompression during kimberlite ascent induces internal stresses in xenoliths requiring volume expansion. High ascent rates imply rapid decompression rates that will exceed normal rates of ductile relaxation in xenoliths. The internal elastic stresses will accumulate promoting tensile failure to produce smaller xenoliths and xenocrysts. Residual stresses (∆σR) depend on ascent velocity (U), the bulk modulus (KT) and viscosity (μ) of the xenolith, and the pressure drop over the ascent distance [z – z0]:
The Atlin Integrated Geoscience Project, jointly funded by federal and provincial governments, en... more The Atlin Integrated Geoscience Project, jointly funded by federal and provincial governments, entered its third and final year in 2002–2003. It is designed to advance understanding of the geological evolution and mineral potential of the northern Cache Creek terrane. Project accomplishments for year three include 1) characterization of Cache Creek Group biostratigraphy and tectonostratigraphy; 2) new surficial geology map outlining placer potential in the Atlin area; 3) improved understanding of the age, composition, emplacement, and metallogenic potential of Mesozoic plutonic rocks; 4) better definition of the distribution and paleoenvironment of Neogene volcanism; 5) delivery of a one-day workshop on magnetic surveying to prospectors and the general public. High-grade copper mineralization was discovered by personnel from the provincial survey. The discovery, named Joss’alun, is hosted within oceanic crustal rocks of the Cache Creek terrane. Mineralization appears concordant with the enclosing volcanic stratigraphy. If syngenetic, it establishes the terrane’s volcanogenic massive sulphide potential. Page 1 Resume : Le projet d’Atlin de l’Initiative geoscientifique ciblee, dont le financement est assure conjointement par les gouvernements federal et provincial, en est a sa troisieme et derniere annee en 2002-2003. Il vise a ameliorer notre comprehension de l’evolution geologique et du potentiel mineral de la partie nord du terrane de Cache Creek. Pendant les trois annees du projet il a ete possible 1) de caracteriser le Groupe de Cache Creek des points de vue biostratigraphique et tectonostratigraphique; 2) de dresser une nouvelle carte geologique des materiaux superficiels delimitant les aires potentielles de placer dans la region d’Atlin; 3) d’ameliorer notre comprehension de l’âge, de la composition, de la mise en place et du potentiel metallogenique des roches plutoniques du Mesozoique; 4) de mieux definir la distribution et le paleoenvironnement du volcanisme neogene; 5) de tenir un atelier d’une duree d’une journee sur les leves magnetiques a l’intention des prospecteurs et du grand public. Une mineralisation cuprifere a haute teneur a ete identifiee par le personnel des services geologiques provinciaux. Cette mineralisation, a laquelle a ete attribue le nom de Joss’alun, est encaissee dans les roches de croute oceanique du terrane de Cache Creek. Par rapport a la stratigraphie volcanique encaissante, la mineralisation semble presenter une relation de concordance. Si elle se revele syngenetique, ceci etablirait pour le terrane un certain potentiel quant aux mineralisations de sulfure massifs volcanogenes. 1 Contribution to the Targeted Geoscience Initiative (TGI) 2000–2003.
... Specifically, we have used the point load strength test (PLST) to measure rock strength and, ... more ... Specifically, we have used the point load strength test (PLST) to measure rock strength and, thereby, track welding intensity in a section of the Bandelier Tuff (Smith & Bailey, 1966; Broxton & Reneau, 1995). PLST is an ideal technique for field studies (eg, Broch & Franklin, 1972 ...
... o.oo INSIGHTS ON WWWBASED GEOSCIENCE TEACHING: CLIMBING THE FIRST YEAR LEARNING CLIFF MICHELL... more ... o.oo INSIGHTS ON WWWBASED GEOSCIENCE TEACHING: CLIMBING THE FIRST YEAR LEARNING CLIFF MICHELLE N. LAMBERSON, MARK JOHNSON, MARY ... with instructors and other students, a site to do selfpaced, directed exercises on important petrolo gic concepts ...
Fine-grained gouge (< 5 microns) is generated along shear zones during the emplacement of daci... more Fine-grained gouge (< 5 microns) is generated along shear zones during the emplacement of dacite domes during the most recent volcanic activity at Mount Saint Helens. Here, we present grain size data from both the natural fault rocks from Mount Saint Helen's and experimentally generated gouge. Our triaxial rock deformation experiments were run at confining pressures (Pc) of 0, 25, 50, and 75MPa, at room temperature and strain rates of ~1 x 10-4/s. We performed experiments that were terminated after failure and experiments on frictional sliding of the gouge. Our starting material has low (6-8%) porosities, a uniform bulk composition (65 wt% SiO2) and is highly. The dacite experiments show a progressive increase in peak strength (100-700 MPa) with increasing Pc and all cores show brittle behavior, characterized by a rapid stress drop. Run products contain macroscopic fractures with deformation extremely localized around the shear fractures. Experimentally deformed dacites show extreme grain size reduction and the production of gouge. Gouge material can reach < 1 micron in diameter. Frictional sliding experiments generated more gouge than experiments stopped after failure. However, there is little modification of the finest grain sizes (<20 microns) because of frictional sliding. We propose that the large stress drop at failure generates the fine-grained gouge and subsequent sliding does not further reduce the grain size. The amount of energy required to produce the fine-grained material is calculated and we compare this to the energy required to generate volcanic ash from fragmentation.
Kimberlite rocks and deposits are the eruption products of volatile-rich, silica-poor ultrabasic ... more Kimberlite rocks and deposits are the eruption products of volatile-rich, silica-poor ultrabasic magmas that originate as small-degree mantle melts at depths in excess of 200 km. Many kimberlites are emplaced as subsurface cylindrical-to-conical pipes and associated sills and dykes. Surficial volcanic deposits of kimberlite are rare. Although kimberlite magmas have distinctive chemical and physical properties, their eruption styles, intensities and durations are similar to conventional volcanoes. Rates of magma ascent and transport through the cratonic lithosphere are informed by mantle cargo entrained by kimberlite, by the geometries of kimberlite dykes exposed in diamond mines, and by laboratory-based studies of dyke mechanics. Outstanding questions concern the mechanisms that trigger and control the rates of kimberlite magmatism.
A recent volcanic eruption occurred at Tseax volcano that formed a series of tephra cones in nort... more A recent volcanic eruption occurred at Tseax volcano that formed a series of tephra cones in northwestern British Columbia, Canada. The explosive to effusive eruption also formed a 32 km long sequence of Fe-rich Mg-poor basanite–trachybasalt lavas covering ∼40 km2. Oral histories of the Nisg_a’a Nation report that the eruption may have caused as many as 2000 fatalities. The actual eruption date and question of whether there was one or multiple eruptive episodes in the 14th and 18th centuries are, as of yet, unresolved. New radiocarbon dating of wood charcoal from immediately beneath vent-proximal tephra deposits and complementary age information suggest an eruption in 1675–1778 CE (95.4% probability) was responsible for the formation of the tephra cone. New paleomagnetic and geochemical data from the tephra cone and lava flows suggest there is, in fact, no statistically significant difference in time between the explosive and effusive deposits and that they formed during a single er...
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